It is of course known to provide ink cartridges for printers with arrangements for optically detecting the level of ink in a chamber or chambers of an ink cartridge. Generally, the optical system includes an optical ink detecting section, such as a prism, in an ink chamber of a cartridge and which is immersed in the ink when the latter is in the chamber above a certain level, and the ink level is read by a light emitting optical unit comprising a light emission device and a photo receptor outside the cartridge. The interface of the optical detecting section extends transverse to the plane of scanning as defined by the light path between the emitter and receptor. If, for example, the scanning takes place in a printer, and the cartridge moves transverse to the direction between the front and rear ends thereof, the plane of the light path between the emitter and receptor is likewise transverse to the direction between the front and rear ends of the cartridge, whereby the light enters the detecting section and reflects off the interface thereof to the receptor. The amount of light which is reflected to the receptor is indicative of the level of ink in the chamber. Such level detecting arrangements are shown, for example, in patents U.S. Pat. No. 5,616,929 to Hara and U.S. Pat. No. 6,361,136 to Watanabe, et al.
It will be appreciated of course that at least the portion of the cartridge in which the level detector is disposed of light transmitting material, and that the light used for determining the ink level can either be visible light or infrared. Ink level detectors such as prisms provided in ink cartridges for use in a single printhead printer are in a single plane of alignment with the plane of the light path of the light emitting optical unit. At the same time, a printer with multiple printheads can have black and color ink cartridges in different scanning or alignment planes. Accordingly, two different ink cartridge configurations are required for use in single and multiple printhead printers. Furthermore, optical prisms provided in cartridges heretofore available are formed integral with the bottom wall of the cartridge and, accordingly, limit the versatility with respect to the plastic materials which can be used for constructing the cartridges.